The book creates a new language, what the authors call a pattern language derived from timeless entities called patterns. As they write on page xxxv of the introduction, "All 253 patterns together form a language." Patterns describe a problem and then offer a solution. In doing so the authors intend to give ordinary people, not only professionals, a way to work with their neighbors to improve a town or neighborhood, design a house for themselves or work with colleagues to design an office, workshop or public building such as a school.

Contents

Written in the 1970s at the University of California, Berkeley, A Pattern Language was influenced by the then-emerging language to describe computer programming and design. "A pattern language has the structure of a network," the authors write on page xviii. Thus, each pattern may have a statement that is referenced to another pattern by placing that pattern's number in brackets, for example: (12) means go to the Community of 7,000 pattern. In this way, it is structured as a hypertext.

It includes 253 patterns such as Community of 7000 (Pattern 12) given a treatment over several pages; page 71 states: "Individuals have no effective voice in any community of more than 5,000–10,000 persons." It is written as a set of problems and documented solutions.

According to Alexander & team, the work originated from an observation that

At the core […] is the idea that people should design for themselves their own houses, streets and communities. This idea […] comes simply from the observation that most of the wonderful places of the world were not made by architects but by the people.

— Christopher Alexander et al., A Pattern Language, front bookflap

The book uses words to describe patterns, supported by drawings, photographs and charts. It describes exact methods for constructing practical, safe, and attractive designs at every scale, from entire regions, through cities, neighborhoods, gardens, buildings, rooms, built-in furniture, and fixtures down to the level of doorknobs. The patterns are regarded by the authors not as infallible, but as hypotheses:

[…] each pattern represents our current best guess as to what arrangement of the physical environment will work to solve the problem presented. The empirical questions center on the problem—does it occur and is it felt in the way we have described it?—and the solution—does the arrangement we propose in fact resolve the problem? And the asterisks represent our degree of faith in these hypotheses. But of course, no matter what the asterisks say, the patterns are still hypotheses, all 253 of them—and are therefore all tentative, all free to evolve under the impact of new experience and observation.

— Christopher Alexander et al., A Pattern Language, p. xv

Some patterns focus on materials, noting that some ancient systems, such as concrete, when adapted by modern technology, may become one of the best future materials:

We believe that ultra-lightweight concrete is one of the most fundamental bulk materials of the future.

— Christopher Alexander et al., A Pattern Language, p. 958

Other patterns focus on life experiences such as the Street Cafe (Pattern 88):

The street cafe provides a unique setting, special to cities: a place where people can sit lazily, legitimately, be on view, and watch the world go by […]. Encourage local cafes to spring up in each neighborhood. Make them intimate places, with several rooms, open to a busy path, where people can sit with coffee or a drink and watch the world go by. Build the front of the cafe so that a set of tables stretch out of the cafe, right into the street.

— Christopher Alexander et al., A Pattern Language, p. 437,439

When these patterns are taken together, the authors say, they begin to form a kind of language, each pattern forming a word or thought of a true language rather than being a prescriptive way to design or solve a problem. As the authors write on p xiii, "Each solution is stated in such a way that it gives the essential field of relationships needed to solve the problem, but in a very general and abstract way—so that you can solve the problem for yourself, in your own way, by adapting it to your preferences, and the local conditions at the place where you are making it."

A notable value is that the architectural system consists only of timeless patterns tested in the real world and reviewed by multiple architects for beauty and practicality. The patterns include provision for future modification and repair, in keeping with the principle that the most satisfying living spaces are those which, like the lives of their occupants, tend to change and evolve over time.

The book values human rights such as freedom, and it shows how architecture can enhance or reduce an individual's sense of freedom

[…] we are saying that a centralized entrance, which funnels everyone in a building through it, has in its nature the trappings of control; while the pattern of many open stairs, leading off the public streets, direct to private doors, has in its nature the fact of independence, free comings and goings.